Apparatus for forming an interproximal interlock



Oct. 3, 1967 A. F. CAMERON 3,344,342

APPARATUS FOR FORMING AN INTERPROXIMAL INTERLOCK Filed April 15, 1964 United States Patent 3,344,842 APPARATUS FOR FORMING AN INTERPROXIMAL INTERLOCK Alan F. Cameron, 3106 Maplewood, Royal Oak, Mich. 48073 Filed Apr. 13, 1964, Ser. No. 359,156 9 Claims. (Cl. 164236) ABSTRACT OF THE DISCLOSURE Interlock forming means for a dental bridge in which a member of continuous cross-section is used to form a groove in one wax pattern and is I'm-bedded in a second wax pattern. When the patterns are used to form the bridge, the member disappears with the second wax pattern, thus resulting in a bridge mold producing an exact tongue-and-groove interlock in the bridge parts.

This application relates to dental bridges and more particularly to a means for forming an interproximal interlock between adjacent portions of a dental bridge, and is of particular utility in the loose-end type of dental bridge.

In situations where a tooth is missing between two remaining teeth, it is sometimes practice to manufacture what is called a loose-end dental bridge to extend across the gap left in the jaw. It is generally the case that the unsupported remaining teeth will lean toward the gap between them, thus making it extremely diflicult to manufacture a bridge of one piece that may easily be inserted in the gap. The usual practice includes the manufacture of a two-piece bridge assembly which may be suitably secured to the live teeth on either side of the gap and which are locked in place upon assembly.

The usual. manner of manufacturing a bridge of this general type involves first the preparation of a model of at least the portion of the jaw containing the remaining teeth and with the gap therebetween, such model being made of plaster and of the exact shape and size as the jaw of the patient. Such model is then placed in a survey instrument so that the model made may be angularly located relative to a vertical probe to find the best angle of insertion and to indicate the manner in which the remaining teeth must be prepared to receive the bridge members. Once the survey has been made, a first wax pattern is formed on the model from which is to be cast an inlay, securable to one of the teeth and forming one of the abutment ends of the bridgeJA second wax pattern is then made which includes the abutment at the opposite end, as well as the false tooth which is to fill the gap between the two abutments. These wax patterns are then utilized to form inlays of gold, or any other suitable material, by the Well known investment process or in any other suitable manner. After the inlays are made, they are again fitted to the model to assure proper fit in the jaw; and after the proper fitting, grinding and the like, the inlay portions may be mounted in the usual manner in the jaw.

It is readily apparent that some suitable means must be provided to secure the two inlays together at their adjacent points. Such interlock is necessary to prevent any relative movement of the two parts which may destroy their mounting to the live teeth or which may create con- I siclerable discomfort to the patient.

There are many types of interlock devices available, most of which are extremely cumbersome and expensive and do not provide the precise accuracy which is necessary under these conditions. Such interlock devices are normally utilized with the wax patterns'and include the 3,344,842 Patented Oct. 3, 1967 formation of a groove in one of the patterns and a means for forming a tab or the like extending from the other pattern and which will be suitably received in the groove in the first member. The basic problems with such interlock devices are that they are extremely small and that they are formed of a plurality of pieces which must be precisely located relative to each other to provide the proper fit. Typical of such interlock devices is the type that provides a U-shaped element that is pressed into the wax pattern forming the first abutment inlay, and a wax tab-forming member which is placed or pressed into the second wax pattern. These are two separate operations; and it is readily apparent that unless the exact dimension, angular relationship, wax pattern temperatures and pressures are maintained, the resultant tab will not properly fit in the resultant groove. This requires a considerable amount of grinding, polishing, fitting and the like in order to properly fit the bridge to the patients jaw.

The device in which this invention is embodied comprises, generally, a plastic body of generally elongate form and which has a continuous cross section of two diflFering shapes. The first shape may be substantially rectangular, and the second portion extending therefrom and contiguous therewith is of substantially enlarged cross section. Extending from the body member is a spindle or post adapted to be mounted in a suitable survey instrument for movement along the axis of the device and in a direction to maintain such movement along a fixed linerelative to the jaw model. The body member is used to form both the groove in the first abutment pattern and the tab extending from the second portion of the bridge; and since it performs both functions, the resultant interlock formed must be of exact and precise dimension, angularity and the like to provide a perfect fit.

The use of such a device greatly simplifies the manufacture of dental bridges of the type described. Such an interlock forming means is extremely simple to manufacture and use, yet provides much greater precision and accuracy than interlock forming devices presently available. Once the inlays are formed from the wax patterns, there must be a precise fit between the interlock members, thus eliminating any grinding, fitting, or polishing operations in order to properly fit the two parts of the bridge together. 7 g V The device may be manufactured of a suitable material which has a melting point substantially the same as the wax used for the wax patterns, so that the device may be incorporated into one or the other of the wax patterns to be compatible with the investment casting, or other process utilized to form the inlay members. I These and other advantages will become more apparent from'the following description and drawing in which: FIGURE 1 is a perspective view of a portion of a jaw having a pair of spaced live teeth with a loose-end type bridge extending therebetween.

FIGURE 2 is an exploded perspective view of the portion of the jaw illustrated in FIGURE 1 to illustrate the shapes of the various parts.

FIGURE 3 is a perspective view of the interlock forming device which forms the interlock connecting the portions of the bridge illustrated in FIGURES 1 and 2.

FIGURE 4 is a schematic view of a survey instrument illustrating its use with a model of a portion of the jaw such as illustrated in FIGURES 1 and 2.

FIGURE 5 is a partial perspective view of a portion of the model illustratedin ,FIGURE 4 showing'one step in the manufacture of the wax pattern for the bridge abutment.

FIGURE 6 is a view similar to FIGURE 5 showing another step in the process of manufacturing the bridge of FIGURES '1 and 2.

Referring more particularly to the drawings, FIGURES 1 and 2 best illustrate the typical loose-end type bridge construction. A portion of the jaw and gum is illustrated generally at and includes a pair of spaced live teeth 12 and 14. For convenience, these teeth may be called the bicuspid abutment tooth 12 and the molar abutment 14; but it is readily understandable that these may be any other teeth in the jaw of the patient. As best shown in FIGURE 2, there is a tooth missing between the live teeth 12 and 14; and it is this gap that must be bridged by a suitable bridge assembly, illustrated generally by the numeral 16. In the usual and accepted practice, live teeth 12 and 14 are suitably formed, as at 18 and 20, respectively, to receive the abutment portions 22 and 24 of the bridge assembly 16 and between which is formed the false tooth 26 which is to fill the gap between the two live teeth.

Bridge assembly 16 is formed, as will be hereinafter described, of inlay members which may be of gold or any other suitable material. The abutment portions 22 and 24 are secured to the live teeth 12 and 14, respectively, in the usual and accepted manner. Connecting the two portions of the bridge 16 is an interlock device which includes a tab 28 extending from the false tooth 26 toward the abutment portion 22. A suitable mating groove 30 is formed in the abutment portion 22 to precisely receive the tab 28 on the false tooth 26. If the angular positioning and dimensions of the tab 28 and groove 30 are precisely maintained, the tab and groove will properly lock the two members together to prevent any movement therebetween and thus destruction of the bridge assembly and/0r discomfort to the user.

In order to form the interproximal interlock 28-30 in the manufacturing process of the bridge assembly 16, an interlock forming device is used such as is best illustrated in FIGURE 3. The interlock device, illustrated generally by the numeral 32, includes an elongate body portion 34 of continuous cross section along its length. Body portion 34 has two definite cross sectional shapes, the first portion 36 having a generally rectangular cross sectional configuration and the second portion 38 having a generally trapezoidal cross sectional configuration. The two portions are contiguous and integral to form the body portion 34. Extending from one end of the body portion 34 is a post or spindle 40 which permits the interlock form ing device. 32 to be properly mounted for its use in such manner as will become hereinafter more apparent. The body member 34 and post 40 may be formed of any suitable material, .although it is preferred that the members he formed of a relatively inexpensive plastic material which may be extruded or injection molded and which is of sufficient rigidity to accomplish the purposes to be hereinafter set forth. It is also desirable that the material have a melting point or burnout point in the temperature range at which the wax from which the patterns are made to form the portions of the dental bridge will melt or burn out of the mold, for purposes to become hereinafter more apparent.

A better understanding of the interlock device may result from a description of its use and the method by which a bridge assembly 16 is formed. As illustrated in FIGURE 4, a model, illustrated generally by the numeral 42, is first made of at least that portion of the jaw which includes the spaced live teeth 12 and 14. These are illus-' trated in FIGURE 4 by the numerals 12' and 14. Such model 42 is constructed in accordance with the usual practice and may be made of any suitable material, such as plaster. Model 42 is mounted on a table 44 which is in turn mounted on a suitable pedestal 46 by means of a ball and'socket or universal joint connection 48. Associated with the pedestal 46 is a screw device 50 which is used. to, lock the ball andsocket connection 48 in the desired position. Pedestal 46 is mountable on a base member 52 forming a part of a survey instrument of the type 4 .generally known in the art. Extending upwardly from base 52' is a post 54 which supports an arm 56 extending over the base 52. Arm 56 supports a spindle 58 mounted in the lower end of which is a probe 60, used to survey the jaw model 42 and indicate the proper line of insertion of the bridge to be constructed. Probe 60 also aids in determining the proper preparation of the abutment teeth 12' and 14'. A suitable thumb screw or the like 62 is provided in the spindle 58 to permit removal, replacement, and securement of the probe 60. In the normal use of such device, the jaw model 42 mounted on the pedestal 46 is properly located beneath the probe 60 and the probe is used to mark or otherwise indicate on the jaw model 42 the proper preparation and angle of insertion of the bridge to be constructed. Once this operation has been completed, the jaw model 42 is locked in place by the screw device 50 and may further be secured or otherwise fixed in position on the base 52 of the survey instrument.

Assuming now that the models of the abutment teeth 12 and 14' have been suitably prepared for receiving the abutment 22 and 24 of the bridge assembly 16, the next step is to prepare the Wax pattern for the portions of the bridge 16 from which the inlays will be made. At this time, the probe 60 is withdrawn from the spindle 58 and the dental interlock forming device 32 is placed in the spindle 58 by means of the post 40 and the thumb screw 62. When properly positioned, the interlock device 32 is lowered into the opening in the model tooth 12 corresponding to the opening 18 in the tooth 12 of FIG- URES l and 2. The device 32 is so positioned that the trapezoidal portion 38 is disposed within the opening and a part of the rectangular portion 36 extends outwardly therefrom toward the second abutment tooth 14'. When thus positioned, the wax pattern to form inlay 22, such pattern being illustrated by the numeral 22 in FIGURE 5, is molded around the interlock device 32 and fills the opening in abutment tooth 12'. The formation of this wax pattern is in accordance with'the well known and usual technique.

Upon completion of the wax pattern 22', the interlock device 32 is withdrawn therefrom by means of the spindle 58, the withdrawal being such that the interlock device 32 moves along a fixed line relative to the jaw model 42. In so doing, the wax pattern 22' is left with a groove 30' which is of exactly the same shape, dimension, and angularity of the interlock forming device 32. The wax pattern 22' may then be used to cast an inlay 22 by the investment process, or in any other suitable manner, in the well known way. 7

After the inlay 22 is completed, it is replaced in the model tooth 12' in the jaw model 42. The interlock forming device 32 is once again lowered into the groove 30' along its fixed line of movement and as such will properly and exactly fit within the groove 30'. As illustrated in FIGURE 6, with the interlock device 32 so located, the major portion of the rectangularly cross sectioned part of the body 34 will extend toward the second abutment tooth 14'. A second wax pattern 24'-26' is then formed in the usual and accepted manner and incorporates the portion of the interlock forming device 32 which extends from the inlay 22. The device 32 remains with and incorporated in the Wax pattern 24-26' so that when the pattern is used to form the inlay 24-26 by the investment or other process, the enlarged part of the interlock portion 32 will act as a pattern tor the tab 28 which extends from the false tooth 26. Since this portion of the interlock device 32 forms the groove 30' in the wax pattern 22', it will now form a tab 28 on the inlay 2426 which is exactly the same in shape, dimension, and angularity as the groove 30 in the inlay 22. Thus, when the two inlay portions 22 and 24-26 are assembled, there will be an exact and precise fit not requiring any grinding, polishing, or other operation to prevent relative movement or improper location of the parts. All that remains is to adjust the occlusal surfaces to their proper shape. The resultant dental bridge structure will exactly fit between the live abutment teeth 12 and 14 for proper securement thereto.

It is readily apparent that it may be desirable somewhere in the process of manufacture to cut oif the interlock forming device 32 at approximately the level of the inlay 22 and the wax pattern of the false tooth 26'. This may be done in any suitable manner; and depending upon the length of the interlock forming device 32, it is also apparent that such device may be used several times before it is fully consumed. Similarly, since the device is formed of a plastic material, it is easily shaped to provide other than the parallel type groove and tab, should such be desirable. Additionally, any other desirable cross sectional configuration may be provided since the device 32 is easily formed by extrusion or injection molding and other shapes and sizes are easily produced. It is also noted that the spindle 58 of the survey instrument may be easily adapted to receive and secure various shapes and sizes of interlock devices of the type described and it may be wholly undesirable to provide a special extension such as post 40.

Thus, an interproximal interlock forming device is provided which is extremely simple to use and is very inexpensive in both use and manufacture. The problems of fitting, grinding, and other operations to properly fit the sections of the bridge assembly together are avoided because of the precise dimensional and angular control in the forming of the interlocking members.

It will be readily apparent after having had reference to the foregoing drawing and description that modifications and alterations in the structure will be easily accomplished. However, it is not intended to limit the scope of the invention by the foregoing drawing and description, but by the scope of the appended claims.

I claim:

1. A device for forming an interlock between first and second inlays in a dental bridge wherein said inlays are formed from first and second wax patterns constructed on a model of at least part of the jaw containing the abutment teeth and wherein said model is fixedly secured on a survey instrument having means thereon for receiving said device and moving said device along a line, said device comprising:

a body portion of continuous cross section, said cross section including a first portion and a second portion;

and a spindle extending along a line parallel to the axis of said body portion and being receivable in said means in said survey instrument for movement along a line fixed with respect to said jaw model;

said device forming a groove in said first wax pattern being received in and extending outwardly from said second wax pattern to form a tab thereon, and being 6 of a material of similar properties to the material of said wax patterns to disappear with said second wax pattern for forming means for exact fitting and interlocking of said first and second inlays formed from said Wax patterns.

2. The device set forth in claim 1 wherein said device is formed of a material having a melting point substantially the same as the melting point of the wax forming said wax patterns.

3. The device set forth in claim 1 wherein said first portion of said cross section is rectangular.

4. The device set forth in claim 1 wherein said second portion of said cross section is trapezoidal.

5. The device set forth in claim 1 wherein said first portion of said cross section is rectangular and said second portion of said cross section is trapezoidal.

6. A device for forming an interlock between first and second inlays in a dental bridge wherein said inlays are formed from first and second patterns, said device comprising:

a body of continuous cross section adapted to be mounted for movement along a line, a portion of said body along one edge thereof being of enlarged 'cross section;

and means for moving said body repeatedly along said line during formation of said first and second patterns to form a groove in said first pattern and a matching tab extending from said second pattern;

whereby, when said inlays are formed from said patterns, said first inlay will be provided with a groove and said second inlay will be provided with a tab of the same shape, dimension, and angular relation as said groove to fit perfectly therein.

7. The device set forth in claim 6 wherein said first and second patterns are formed of wax and said body is formed of a material having substantially the same melting point as said Wax.

8. The device set forth in claim 6 wherein said portion of said body along one edge thereof is of trapezoidal cross sectional configuration with the longer base thereof being along the outer edge of said body.

9. The device set forth in claim 8 wherein the remainder of said body is of rectangular cross sectional configuration.

References Cited UNTTED STATES PATENTS 1,520,809 12/1924 Cohen 32-4 FOREIGN PATENTS 540,053 2/1956 Italy.

I. SPENCER OVERHOLSER, Primary Examiner. E. MAR, Assistant Examiner. 

6. A DEVICE FOR FORMING AN INTERLOCK BETWEEN FIRST AND SECOND INLAYS IN A DENTAL BRIDGE WHEREIN SAID INLAYS ARE FORMED FROM FIRST AND SECOND PATTERNS, SAID DEVICE COMPRISING: A BODY OF CONTINUOUS CROSS SECTION ADAPTED TO BE MOUNTED FOR MOVEMENT ALONG A LINE, A PORTION OF SAID BODY ALONG ONE EDGE THEREOF BEING OF ENLARGED CROSS SECTION; AND MEANS FOR MOVING SAID BODY REPEATEDLY ALONG SAID LINE DURING FORMATION OF SAID FIRST AND SECOND PATTERNS TO FORM A GROOVE IN SAID FIRST PATTERN AND A MATCHING TAB EXTENDING FROM AND SECOND PATTERN; WHEREBY, WHEN SAID INLAYS ARE FORMED FROM SAID PATTERNS, SAID FIRST INLAY WILL BE PROVIDED WITH A GROOVE AND SAID SECOND INLAY WILL BE PROVIDED WITH A TAB OF THE SAME SHAPE, DIMENSION, AND ANGULAR RELATION AS SAID GROOVE OF FIT PERFECTLY THEREIN. 